🏷️ Basic Information

Make:

Mercedes-Benz

Model:

W126 SEC

Model Year:

1990

Generation Code:

C126 (Second Generation)

Body Style Code:

SEC (Coupe)

👋 Introduction

Positioning:

The W126 SEC coupe represented the pinnacle of Mercedes-Benz luxury and engineering in its era, blending performance with unparalleled comfort and build quality.

Competitors:

Competed directly with high-end luxury coupes from brands like BMW (e.g., 8 Series), Jaguar, and Rolls-Royce.

Design:

Iconic pillarless hardtop coupe design, aerodynamic styling, extensive use of premium materials.

Value Proposition:

Provides dealership-level repair and maintenance information, enabling owners to perform complex tasks efficiently and accurately, thus saving significant costs on professional servicing.

Usability:

Consolidated into a single, easy-to-use PDF, eliminating the need for multiple physical manuals and offering searchability and selective printing.

📋 Manual Details

Primary Coverage:

Complete Service and Repair for the 1990 Mercedes-Benz W126 SEC Coupe

Model Variants Covered:

All 1990 W126 SEC models

Estimated Page Count:

Comprehensive (Exact count not specified, but implied extensive)

Type:

Factory Service and Repair Manual

Language:

English

Format:

Digital (PDF)

📖 Manual Coverage

Engine Mechanical:

Engine overhaul, cylinder head, piston rings, crankshaft, camshafts, valve train, timing system

Engine Management:

Fuel injection (KE-Jetronic/Lambda), ignition system, engine control unit (ECU) diagnostics, sensors, actuators

Cooling System:

Radiator, water pump, thermostat, cooling fan, hoses, coolant specifications

Lubrication System:

Oil pump, oil filter, oil pan, oil specifications, lubrication points

Emission Control:

Catalytic converter, EGR system, emission sensors, diagnostic procedures for emission faults

Intake Exhaust:

Intake manifold, exhaust manifold, exhaust system components, gaskets

Automatic Transmission:

4-speed automatic transmission (e.g., 722.3/722.4), valve body, torque converter, clutch packs, fluid specifications, adjustments

Manual Transmission:

Not applicable for SEC models, but if mentioned for general W126, would cover 5-speed manual transmission (e.g., G3/36)

Drive Axle Differential:

Rear axle, differential service, axle shafts, universal joints, fluid specifications

Suspension:

Front and rear suspension components, shock absorbers, springs, control arms, ball joints, bushings, alignment specifications

Brakes:

Front and rear disc brakes, brake calipers, brake pads, brake rotors, brake fluid specifications, ABS (Anti-lock Braking System) diagnostics and repair

Parking Brake:

Parking brake mechanism, cables, adjustments

Steering:

Steering column, power steering system, steering gear, steering linkage, power steering fluid specifications, hydraulic pressure tests

Climate Control:

Air conditioning system, HVAC controls, refrigerant, compressor, evaporator, condenser, blower motor, climate control diagnostics and repair

Electrical System:

Battery, alternator, starter, lighting system, fuses, relays, wiring harness schematics, troubleshooting

Instrumentation Controls:

Instrument cluster, gauges, warning lamps, switches, controls

Body Exterior:

Doors, hood, trunk, windows, mirrors, body panels, trim, seals

Body Interior:

Seats, upholstery, door panels, headliner, dashboard, carpeting

Supplemental Restraint:

Airbag system diagnostics and repair (if equipped)

Cruise Control:

Cruise control system operation, diagnosis, and repair

Wiper Washer:

Wiper system, washer system, components, and troubleshooting

Door Locks:

Central locking system, door lock mechanisms, remote locking (if equipped)

Audio Visual:

Factory radio/audio system troubleshooting and repair

Multiplex Can:

Information on multiplex communication systems, if applicable to the 1990 model year

Maintenance:

Scheduled maintenance, fluid changes, filter replacements, tune-ups

Diagnostics:

Troubleshooting guides, diagnostic flowcharts, fault code interpretation

Repair:

Detailed step-by-step repair instructions for all covered systems

Installation:

Component replacement and installation procedures

Adjustment:

Alignment, brake adjustments, shift linkage adjustments

Depth:

Complete, from basic maintenance to advanced diagnostics and full component overhaul

Detail Level:

Factory-level detail, including torque specifications, clearance measurements, and specialized tool requirements

Illustrations:

Extensive diagrams and illustrations for visual guidance

Wiring Schematics:

Complete and detailed wiring diagrams for all electrical systems

📊 Manual Specifications

Format:

PDF

Printability:

Fully printable, allowing users to print specific pages or sections

Image Scalability:

Images can be enlarged for detailed viewing and printing

Binding Type:

Digital (no physical binding)

Paper Type:

N/A (Digital format)

Reader:

Adobe PDF Reader (free)

Compression:

Winzip (free online)

Operating Systems:

Windows (Vista 32/64, XP, ME, 98, NT, 2000) and Mac OS

⚙️ Engine Specifications

Engine Code:

Likely M117 (5.0L V8) or M119 (5.0L V8 DOHC) depending on specific sub-model within the 1990 SEC range.

Displacement:

Typically 5.0 liters (4973 cc) for V8 models of this era.

Horsepower Est:

Approximately 240-270 hp (depending on engine variant and emissions controls).

Torque Est:

Approximately 300-340 lb-ft (depending on engine variant).

Fuel Delivery:

Bosch KE-Jetronic or KE3-Jetronic (CIS-E) fuel injection system with Lambda control.

Ignition Type:

Electronic ignition with distributor and ignition coil.

🔧 Transmission

Transmission Type:

4-speed Automatic Transmission (e.g., 722.3 or 722.4)

Transmission Type:

Not typically offered with a manual transmission in SEC models.

Transmission Features:

Comfort-oriented shift points, potentially with a sport/economy mode selector.

📐 Dimensions

Length:

Approximately 5,012 mm (197.3 in)

Width:

Approximately 1,798 mm (70.8 in)

Height:

Approximately 1,397 mm (55.0 in)

Curb Weight Est:

Approximately 1,750 kg (3,858 lbs)

Wheelbase:

Approximately 2,850 mm (112.2 in)

🛡️ Safety Features

Safety Ratings:

While official crash test data from modern standards is not available for this era, the W126 was known for its robust construction, safety cage, and extensive passive safety features.

ABS:

Standard Anti-lock Braking System (ABS).

Airbags:

Driver's side airbag was becoming standard or a common option in this model year.

Seatbelts:

Three-point seatbelts for all occupants, potentially with front seatbelt pre-tensioners.

Body Structure:

Reinforced safety cell, crumple zones.

💡 Technology Features

Audio System:

Factory premium audio system, often with cassette player and analog tuning. Some models may have optional CD changer.

ABS:

Advanced for its time, the ABS system is a key driver assistance feature.

Connectivity:

Limited by modern standards, primarily focused on vehicle systems. No integrated Bluetooth or Wi-Fi.

Climate Control Type:

Automatic climate control with optional multi-zone functionality.

🔧 Maintenance

Oil Change Interval:

Typically every 15,000 km (9,000 miles) or 12 months, whichever comes first, using synthetic oil.

Major Service Interval:

Comprehensive inspections and component checks at regular intervals, often detailed in specific service schedules within the manual.

Engine Oil:

Refer to manual for specific viscosity (e.g., Mobil 1 15W-50 or similar synthetic recommended for this era, or manufacturer-specified MB 229.1/229.5 if applicable).

Transmission Fluid:

MB 236.1 or equivalent automatic transmission fluid (e.g., Dexron III compatible).

Coolant:

Mercedes-Benz approved coolant (e.g., G05 or equivalent OAT/HOAT coolant mixed with distilled water).

Brake Fluid:

DOT 3 or DOT 4 brake fluid.

Common Issues:

Wiring harness degradation (especially brittle insulation), vacuum leaks, fuel distributor issues, climate control system faults (e.g., HVAC blower motor resistor), window regulator problems, seized brake calipers due to age.

📚 Vehicle History

Heritage:

Mercedes-Benz has a long-standing reputation for building high-quality, durable, and technologically advanced vehicles, particularly in the luxury segment.

W126 Evolution:

The W126 chassis was produced from 1979 to 1991, with the C126 SEC coupe variant being introduced in 1981. The 1990 model represents a later iteration of this highly successful and refined platform.

Production Era:

1979-1991 (W126 Sedan), 1981-1991 (C126 SEC Coupe)

🏆 Awards & Recognition

Historical Recognition:

The W126 series, including the SEC coupe, was widely lauded by automotive journalists and critics for its comfort, build quality, and engineering excellence, frequently topping luxury car comparison tests of its era.